Delay in development of language skills, adaptive skills and cognitive skills mark the onset of intellectual disability. In mild cases, signs and symptoms may not be noticeable until the child reaches preschool age. The following are some of the important markers noticed in affected children:

• Inability to speak mama/dada in the first year
• Child does not say 2 word phrases by the age of 2 years
• Delay in motor adaptive skills such as child does not dress up or practices such as self-feeding and or toileting are absent
• Delay in cognitive development, marked by inability of the child to follow instructions and lack of problem solving skills
• Behavioral disturbances are noticeable such as hyperactivity, disturbance in sleep and colic

• Cerebral Palsy

  […] for Cerebral Palsy and Developmental Medicine (AACPDM). schema:workExample http://dx.doi.org/10.1111/(ISSN)1469-8749 > ; umbel:isLike http://d-nb.info/020059965 > ; wdrs:describedby http://www.worldcat.org/title/-/oclc/637828095 > ;. [worldcat.org]

  palsy (n = 100, 2.0%). [ncbi.nlm.nih.gov]

  Assessment checklist for various disabilities namely cerebral palsy, hearing impairement, mental retardation, visually impairement and learning disability are available for identifying special needs of children studying in an inclusive education setup [play.google.com]

  Features Associated With MR Feature Mild MR Moderate-severe MR Seizures 12% 35% Cerebral Palsy 9% 20% Blindness 1% 15% Deafness 7% 10% Table 2. [thedoctorwillseeyounow.com]

  palsy ( n = 100, 2.0%). [doi.org]

• Trisomy 21

  In Trisomy 21, the affected child inherits three chomosome 21's. [thedoctorwillseeyounow.com]

  For example, if a baby is born with three #21 chromosomes, rather than the usual pair, the baby would be said to have "trisomy 21". Trisomy 21 is also known as Down syndrome. Other examples of trisomy include trisomy 18 and trisomy 13. [chw.org]

  The characteristic phenotype of Down syndrome is basically the same in trisomy 21 and in translocation. [emedicine.com]

• Weakness

  The symptoms of both patients started as weakness of the unilateral upper limb and neck, and extended to bulbar and respiratory weakness in a relatively short period. Of note, the first patient was mentally retarded before the onset of weakness. [ncbi.nlm.nih.gov]

  […] communicating, walking, self feeding, toilet learning, and social interaction Intellectual function is significantly below average Middle Childhood and Adolescence Developmental delays are usually clear by this age Evaluation can identify strengths and weaknesses [brightfutures.org]

  […] tumor Some children show differences at birth or shortly after birth, such as: Unusual facial features or a head that’s unusually large or small Unusually shaped hands or feet Sometimes children may have signs of a health problem, such as: Seizures, weakness [merckmanuals.com]

  This definition is accompanied by an assessment of a person's strengths and weaknesses in adaptive skills for daily living and the resulting support services that the person needs. [dfps.state.tx.us]

• Swelling

  An infection of the membrane covering the brain (meningitis) or an inflammation of the brain itself (encephalitis) cause swelling that in turn may cause brain damage and mental retardation. [medical-dictionary.thefreedictionary.com]

  An infection of the membrane covering the brain (meningitis) or an inflammation of the brain itself (encephalitis) can cause swelling that in turn may cause brain damage and mental retardation. [minddisorders.com]

  The infectious brain diseases like meningitis or encephalitis can impose unwanted swelling in the brain, which can lead to brain damage and mental retardation. [momjunction.com]

• Progressive Intellectual Disability 

  The patient was an 11-year-old girl with onset of seizures at the age of 18 months and followed by progressive intellectual disability (ID) later. [ncbi.nlm.nih.gov]

  Milder cases of progressive intellectual disability can sometimes be traced to economic and environmental deprivation early in childhood—conditions that are associated with poverty or famine. [britannica.com]

• Failure to Thrive

  The patient presented with exocrine pancreatic insufficiency as well as failure-to-thrive. On dysmorphological examination, she was noted to have an abnormal hair pattern with frontal upsweep and alae nasi hypoplasia. [ncbi.nlm.nih.gov]

  Clinical manifestations (eg, failure to thrive, lethargy, vomiting, seizures, hypotonia, hepatosplenomegaly, coarse facial features, abnormal urinary odor, macroglossia) may suggest a genetic metabolic disorder. [merckmanuals.com]

  Translated by Apolline Morville B.2 Failure to thrive or weight faltering in a primary health care setting (824 KB PDF) Astrid Berg VERSION IN FRENCH: “ Retard de croissance ou prise de poids hésitante en contexte de soin de santé primaire ” (1.27 MB [web.archive.org]

• Poor Oral Hygiene

  CONCLUSION: The deteriorated teeth condition and deprived periodontal health of MR patients may be most likely caused by the poor oral hygiene and may be worsen with the severity of the MR. [ncbi.nlm.nih.gov]

• Visual Impairment

  Assessment checklist for various disabilities namely cerebral palsy, hearing impairement, mental retardation, visually impairement and learning disability are available for identifying special needs of children studying in an inclusive education setup [play.google.com]

  The various eye abnormalities can potentially lead to varying degrees of visual impairment. [rarediseases.org]

  Speech, hearing and visual impairment. Epilepsy. Urinary and faecal incontinence. [web.archive.org]

  Sensory: This is done to determine if there are any visual impairments or hearing defects, as they are more commonly seen in children with mental retardation. [newhealthguide.org]

  Speech, hearing and visual impairment. Epilepsy. Urinary and faecal incontinence. Increased risk of obesity, fractures. Poor oral health (including dental caries and loss of teeth). [patient.info]

• Impulsivity

  Abstract Hyperactivity syndromes and disorders (ADHD and HKD) include the symptoms of overactivity, inattention, and impulsivity, which occur in many other mental disorders as well, including mental retardation (MR). [ncbi.nlm.nih.gov]

  […] interacting with others If your child has ID, they will probably experience some of the following behavioral issues: aggression dependency withdrawal from social activities attention-seeking behavior depression during adolescent and teen years lack of impulse [helpingchildclinic.com]

  […] pictures Attention Deficit Hyperactivity Disorder- : Attention Deficit Hyperactivity Disorder- dysfunction of central nervous system leading to problems in attention not focus on one task display behavioural problem along with poor academic performance impulsivity [authorstream.com]

  There is social withdrawal in both the disorders but in autism there is inability of communication due to delayed impulse transmission whereas in mental retardation there is loss of cerebral functioning responsible for all poor development of all skills [differencebetween.net]

  Turkish] Mehmet Emrah Karadere, Ece Yazla, Hüseyin Şehit Burhan, Ebru Turgal, Tacettin Kuru, Mehmet Hakan Türkçapar Anadolu Psikiyatri Derg. 2020; 21(3): 269-276 » Abstract » PDF» doi: 10.5455/apd.82968 The relationship between metabolic syndrome and impulsivity [anadolupsikiyatri.net]

• Behavior Disorder

  ASSOCIATED PROBLEMS • Self injury • Pica • CP • Epilepsy • Toilet probs • Sleep disorders • Eating problems • Poisoning • Sexual abuse • Learning disorders • Behavior problems 10. [slideshare.net]

  Finally, it is the behavioral disorder and not intellectual retardation that is decisive and destructive to family life. [amazon.com]

  The association of reading disability, behavioral disorders, and language impairment among second-grade children. Journal of Child Psychology and Psychiatry and Allied Disciplines, 41, 473 — 482. [doi.org]

  Obsessive-compulsive disorder, conduct disorder, tic disorders, and other stereotypic behaviors are also diagnosed more commonly in those with MR/ID. [emedicine.com]

• Aggressive Behavior

  The patient was a 20-yr-old male with chief complaints of continuous masturbation, genital exposure, and aggressive behavior that started 2 yr ago. [ncbi.nlm.nih.gov]

  Symptoms: Signs and symptoms of intellectual disability include delay in development of cognitive skills, motor skills, language delays, continuation of infant type behavior till late years, difficulty in following instructions and aggressive behavior [symptoma.com]

  The excess is particularly marked within the domains of anxiety and depression, aggressive behavior, inattention, social difficulties, and social withdrawal (P. Hoare, unpublished data). [ajnr.org]

• Anxiety Disorder

  From anxiety disorders, depression and ADHD to autism and developmental delays, we get to the heart of your child’s condition, using the latest diagnostic tools and therapeutic procedures. [floridahospital.com]

  ANXIETY DISORDERS Associate Editor: Cesar Soutullo F.1 Anxiety disorders in children and adolescents: nature, development, treatment and prevention (632 KB PDF) Ronald M Rapee VERSION IN FRENCH: “ Troubles anxieux chez l’enfant et l’adolescent. [web.archive.org]

  Major depression, bipolar disorders, anxiety disorders, and other mood disorders are the most common psychiatric diagnoses in adults with MR/ID. [emedicine.com]

• Delusion

  His medical history included psychosis, suicidal depression, paranoid delusions, and self-mutilation. [hrw.org]

  (Fernald, 1902, p. 489). 289 There was much self-delusion and falsification of facts regarding maintenance costs, and I found it difficult to distinguish between claims as to how many residents were discharged as self-supporting; how many were considered [disabilitymuseum.org]

• Amenorrhea

  Our case provides evidence for an association of primary amenorrhea and mental retardation with concomitant unbalanced X-autosome translocation and X chromosome rearrangement. [ncbi.nlm.nih.gov]

• Neglect

  To make complaints about long term care facilities and resident abuse, mistreatment, neglect, or financial exploitation contact DHCQ via their Complaint and Incident Reporting information. [dhss.delaware.gov]

  […] fragile X syndrome, Williams syndrome and Prader Willi syndrome problems during pregnancy such as infections or exposure to alcohol, drugs or other toxins problems at birth environmental factors such as exposure to poisons, lead or mercury consequences of neglect [web.archive.org]

  Causes include: Head injury Brain infection Emotional abuse and neglect Brain tumor Some children show differences at birth or shortly after birth, such as: Unusual facial features or a head that’s unusually large or small Unusually shaped hands or feet [merckmanuals.com]

  Severe head injury, near-drowning, extreme malnutrition, infections in the brain, exposure to toxic substances such as lead, and severe neglect or abuse can also cause it. None of the above. [webmd.com]

• Tantrums

  Your child may have: Language problems, such as a later start using words or speaking in full sentences Trouble making friends and other social skills Trouble dressing and doing other self-care tasks Sometimes, behavior problems such as temper tantrums [merckmanuals.com]

  […] sitting up and walking Late start in talking or difficulty in talking Late in getting potty trained, doing activities like dressing or feeding independently Difficulty in remembering things or associating actions with corresponding consequences Throwing tantrums [newhealthguide.org]

  […] walking late Talking late or having trouble with talking Slow to master things like potty training, dressing, and feeding himself or herself Difficulty remembering things Inability to connect actions with consequences Behavior problems such as explosive tantrums [webmd.com]

• Profound Intellectual Disability

  […] effects on persons with severe profound intellectual disabilities. [tamuct.edu]

  Severe or profound intellectual disability – a person with severe intellectual disability will have a 20 to 35 IQ score. A person with profound intellectual disability will have an IQ score up to 20. [web.archive.org]

• Irritability

  The cornea is the clear (transparent) outer layer of the eye, and has two functions – it protects the rest of the eye from dust, germs and other harmful or irritating material, and it acts as the eye’s outermost lens, bending incoming light onto the inner [rarediseases.org]

  Fecal transplant is used to treat gut infections and is now being studied as a treatment for obesity, urinary tract infections, irritable bowel syndrome and more. [nytimes.com]

  But I'm glad to see that non-disabled people are beginning to understand why less offensive words such as 'special', 'brave' and 'wheelchair-bound' are so irritating to many disabled people. [web.archive.org]

  Vomiting Hypoglycemia Seizure Lethargy, irritability Poor weight gain Hepatic failure Splenomegaly Mental retardation Ascitis 22. [slideshare.net]

  Buspirone in the management of anxiety and irritability in children with pervasive developmental disorders: results of an open-label study. J Clin Psychiatry. 1998 ; 59 : 56 – 59 ↵ Kowatch RA, DelBello MD. [doi.org]

• Delayed Milestone

  In mental retardation, the child tends to have delayed milestones and will be slow in talking and walking. The low IQ restricts the memory and children have lower than average learning abilities and problem solving skills. [differencebetween.net]

  […] to hypoplastic facial features, developmental delay, small stature and familial resemblance. [aafp.org]

Based on the guidelines provide by the Diagnostic and Statistical Manual of Mental Disorders, the child should meet the following three criteria to be diagnosed with intellectual disability.

• Limitations in adaptive behavior such as interpersonal skills, communication and self-help skills
• Deficits in mental abilities
• Signs and symptoms become evident early in life

The first 2 factors can be diagnosed by measuring the IQ score. The third factor is important to determine, in order to rule out other disorders like Alzheimer disease which share similar signs and symptoms, but have a late onset.

An IQ score of below 70 indicate mental retardation and is done at the preliminary level. This is followed by other methods such as adaptive behavior rating scale and Denver developmental screening test [8].

Brain imaging tests are also indicated in children with intellectual disability. A MRI scan of brain is preferred, because it enables better assessment of abnormalities of central nervous system [9].

Treatment is geared towards maximum development of the child’s potential. Therapists and specialized educators help in fulfilling such goals. They help in developing the social skills of the child so that they learn to communicate effectively and put forth their problems and thoughts to the outside world. Behavior counseling forms an important part of the treatment regime to help the child to deal with their mood swings and sometimes aggressive nature.

Pharmacologic treatment is of little help in improving the cognitive functioning. However, the drug donezepil has been found to be effective in improving the cognitive function in children with Down syndrome. Parents might also think of enrolling their children in various support groups for proper grooming [10].

Prognosis of the condition would largely depend on the underlying etiology, severity of the disease and type of treatment methods administered. In many cases it has been seen that, affected individuals lead a productive life and learn to carry out many tasks on their own. With proper learning and education, children can function properly and can be successful in life [7].

Amongst the various etiologies, Down syndrome, fetal alcohol syndrome and velocariofacial syndrome are the major causative factors [2]. In about one third to the half of all cases, the exact cause behind development of mental retardation is not known [3].

The following causes are known to trigger the onset of mental retardation:

• Infections that occur during birth or after it
• Chromosomal abnormalities
• Malnutrition during pregnancy 
• Alcohol consumption during pregnancy can cause improper fetal development
• Exposure to disease conditions such as measles, pertussis and meningitis
• Iodine deficiency 
• Absence of arcuate fasciculus

Mental retardation affects about 1 – 3% of the total population. The prevalence rate of severe form of intellectual disability has been estimated to occur in 6 per 1,000 population [4].

It has been assessed that, about 75 – 90% of individuals suffer from mild form intellectual disability. Of these, non-syndromic intellectual disability occurs in about 30 – 50% of cases. Boys are found to be more affected than girls, for both mild and severe form of the disease. Mortality rates at an early age have been found to be higher in children suffering from Down syndrome [5].

Mental retardation primarily occurs as the outcome of several disorders of the central nervous system. In majority of the cases, no significant structural abnormalities have been noticed in individuals with mild intellectual disability. However, in severe cases, malformations of the central nervous system include hydranencephaly, neural tube defects and microcephaly. Certain studies have indicated a link between poor cognitive functioning and poverty; however the etiologic contribution still remains unclear [6].

Some of the risk factors such as alcohol consumption during pregnancy, avoiding toxin exposure and iodine deficiency can go a long way in preventing the onset of mental retardation. Getting vaccinated against infectious diseases such as rubella can also help prevent mental retardation from setting in. Proper genetic counseling during pregnancy can help parents take informed decisions.

The condition is diagnosed before one reaches 18 years. Individuals suffering from mental retardation lack in appropriate mental development and do not have the ability to adapt and learn new things. Intellectual disability is further classified into 2 categories: non-syndromic intellectual disability and syndromic intellectual disability [1].

• Definition: Mental retardation, also known as intellectual disability, is a type of neuro-developmental disorder, wherein there is impairment of adaptive functioning and intellectual skills. Affected individuals have an IQ score of 70 or below.
• Cause: Various disease conditions such as Down syndrome, fetal alcohol syndrome and velocariofacial syndrome predisposes children to develop intellectual disability. In addition, various other risk factors include alcohol consumption during pregnancy, exposure to toxins, infectious diseases, iodine deficiency, chromosomal abnormalities and malnutrition.
• Symptoms: Signs and symptoms of intellectual disability include delay in development of cognitive skills, motor skills, language delays, continuation of infant type behavior till late years, difficulty in following instructions and aggressive behavior.
• Diagnosis: Diagnosis includes assessing the IQ score and testing the adaptive behavior of the individual with help of adaptive behavior rating scale. In addition, imaging studies like CT scan and MRI of brain is also required to assess abnormalities.
• Treatment: Treatment is geared towards developing the potential of the children as much as possible. This is done by therapists and specialized educators who provide training and behavior counseling to help develop their skills. Some medications such as donezepil have been found to be effective for patients with Down syndrome; it helps improve their cognitive functioning.

1. Biscaldi M, Rauh R, Irion L, Jung NH, Mall V, Fleischhaker C, et al. Deficits in motor abilities and developmental fractionation of imitation performance in high-functioning autism spectrum disorders. Eur Child Adolesc Psychiatry. Oct 2 2013
2. American Academy of Pediatrics Committee on Genetics. Health Supervision for Children with Down Syndrome. Pediatrics. February 2001,;volume 107, number 2,:pages 442-449
3. Croen LA, Grether JK, Selvin S. The epidemiology of mental retardation of unknown cause. Pediatrics 2001; 107:E86.
4. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders.5th Edition. Washington, DC: APA Press; 2013.
5. Kaufman L, Ayub M, Vincent JB. The genetic basis of non-syndromic intellectual disability: a review. J NeurodevDisord 2010; 2:182.
6. Ramer JC, Miller G. Overview of Mental Retardation. In: Static Encephalopathies of Infancy and Childhood, Miller G, Ramer JC (Eds), Raven Press, New York 1992.
7. vanKarnebeek CD, Scheper FY, Abeling NG, et al. Etiology of mental retardation in children referred to a tertiary care center: a prospective study. Am J Ment Retard 2005; 110:253.
8. Majnemer A, Shevell MI. Diagnostic yield of the neurologic assessment of the developmentally delayed child. J Pediatr 1995; 127:193.
9. Bouhadiba Z, Dacher J, Monroc M, et al. [MRI of the brain in the evaluation of children with developmental delay]. J Radiol 2000; 81:870.
10. McConkey R, Kelly F, Mannan H, Craig S. Moving from family care to residential and supported accommodation: national, longitudinal study of people with intellectual disabilities. Am J Intellect Dev Disabil 2011; 116:305.